In the prior art a mandrelizing process was used for cold expanding fastener holes. It was cumbersome due to its two-sided operation, requirements for mandrel and hole lubrication, and excessive mandrel breakage. Although recent lubrication improvements have reduced galling and seizing problems, and a one sided mandrel has been developed, the mandrelizing process remains relatively costly due to the labor intensive operation and the need for mandrel and hole lubrication.
The development of a prelubricated split sleeve, used on the mandrel, permitted the development of one-sided operation in which the mandrel was extended through the drilled hole. A split sleeve was carried on a small diameter portion of the mandrel and was moved into the hole and the mandrel was pulled through the hole to cold-work the metal surrounding the hole with the split sleeve in place.
The process as developed included separate post reaming and countersinking operations. Post reaming was required to accommodate the wide variance in fastener interferences. While not based on fatigue test results, there was also a perceived requirement to remove a ridge left by the split in the sleeve. Fatigue test results dictated the need for separate countersink operation after cold-working of a straight hole. The increased usage of the split sleeve process has highlighted the desirability of eliminating these separate operations.
The basic patent relating to cold-expansion of fastener holes, by use of a split lubricated spacing sleeve, is U.S. Pat. No. 3,566,662, granted Mar. 2, 1971, to Louis A. Champoux, and entitled Coldworking Method And Apparatus. A Method And Apparatus For Making Sleeves is disclosed in U.S. Pat. No. 3,665,744, granted May 30, 1972, to Clair M. Harter. It should be noted that there are also cold-working sleeves in use that are not split. U.S. Pat. No. 3,892,121, granted July 1, 1975, to Louis A. Champoux, Horace E. Hill and Joseph L. Phillips, and entitled Apparatus For Cold-Working Holes, discloses a form of mandrel and mandrel pulling tool and gun. U.S. Pat. No. 4,187,708, granted Feb. 12, 1980, to Louis A. Champoux entitled Pulling Apparatus And Method, discloses a preferred form of pull gun.
A paper, entitled "Fatigue Improvement by Sleeve Coldworking by Joseph L. Phillips is also of interest.
U.S. Pat. Nos. 3,949,535 and 4,164,807 to John O. King, Jr. indicate, in column 2, lines 29-44 in the first patent and lines 32-46 in the second patent, that two problems are encountered using a split sleeve. The first is that the interruption of the tubular member surface at the split produces a reduced compressive stress gradient along the material at the surface of the hole and the second is that because the tubular member is allowed to move slightly axially within the hole during the cold-working operation, the axially oriented tensile stress gradient is still induced into the surface grain of the material about the hole. Thus, the desirable compressive stress gradient induced into the material at the surface of the hole is partially offset by the lower compressive stress gradient occurring at the split in the sleeve and secondly by the axially oriented tensile stress gradient induced in the grain of the material at the surface of the hole.
Further, in column 11, lines 57-65 in the first patent and lines 55-64 in the second patent, it is stated that in the prior art technique of expanding holes through the workpiece using a split tubular member, it will be seen from FIG. 23 that a discontinuity in the uniform stress gradient pattern is induced in the workpieces about the hole in the area of the split. It will also be noted that as the hole is expanded further, the discontinuity in the stress gradient of the prior art split tubular member cold-working technique induces an even wider discontinuity in the stress gradient.
The King, Jr. Pat. Nos. 3,949,535 and 4,164,807 have additional information, more pertinent and contrary to the teachings of the present invention. In column 2, in both of the patents, starting at line 63 in the first patent and line 65 in the second patent, it is stated that a hole sizing technique that has been attempted is to drill a pilot hole and then pull a mandrel with an expansion section thereon through the pilot to finally size the same. Because the material of the workpieces rebounds after the passage of the mandrel through the holes and the amount of rebound is a function of the amount the pilot hole is enlarged, it is necessary to accurately size the holes either before or after the enlarging operation with a tool such as a reamer in order to accurately determine the final hole size. Thus, because of the inability to accurately control the reaming operation when using manually held tools, this technique has been unable to accurately size holes.
The statements in the King, Jr. patents have been proven incorrect in prior split sleeve operations and in the development and testing relating to the present invention.
Other more recent pertinent inventions are described in U.S. Patent Applications: Apparatus And Method For Prestressing A Countersunk Fastener Hole, Ser. No. 273,725, by Louis A. Champoux, filed June 15, 1981, now Pat. No. 4,423,619; Method And Apparatus For Prestressing Fastener Holes, Ser. No. 347,717, by Robert L. Champoux et al, filed Feb. 10, 1982, now Pat. No. 4,471,643; and Apparatus Having Extended Prestressing And Sleeve Retaining Devices For Prestressing Countersunk Fastener Holes And Method, Ser. No. 347,739, by Louis A. Champoux, filed Feb. 10, 1982, now Pat. No. 4,425,780.
Other known prior art is as follows:
U.S. Pat. No. 1,647,447, granted Nov. 1, 1927, to G. J. Hartnett;
U.S. Pat. No. 1,648,189, granted Nov. 8, 1927, to L. Ottinger;
U.S. Pat. No. 2,459,808, granted Jan. 25, 1949, to G. A. Geyer;
U.S. Pat. No. 3,056,197, granted Oct. 2, 1962, to R. G. Lawson;
U.S. Pat. No. 3,157,305, granted Nov. 17, 1964, to C. W. Baugh;
U.S. Pat. No. 3,270,410, granted Sept. 6, 1966, to L. Salter et al;
U.S. Pat. No. 3,596,491, granted Aug. 3, 1971, to H. A. Cress;
U.S. Pat. No. 3,683,658, granted Aug. 15, 1972, to R. C. Roeschlaub;
U.S. Pat. No. 3,693,247, granted Sept. 26, 1972, to C. K. Brown;
U.S. Pat. No. 3,805,578, granted Apr. 23, 1974, to J. O. King, Jr.;
U.S. Pat. No. 3,835,688, granted Sept. 17, 1974, to J. O. King, Jr.;
U.S. Pat. No. 3,879,980, granted Apr. 29, 1975, to J. O. King, Jr.;
U.S. Pat. No. 3,943,748, granted Mar. 16, 1976, to J. O. King, Jr.;
U.S. Pat. No. 3,949,535, granted Apr. 13, 1976, to J. O. King, Jr.;
U.S. Pat. No. 4,127,345, granted Nov. 28, 1978, to D. J. Angelosanto et al;
U.S. Pat. No. 4,164,807, granted Aug. 21, 1979, to J. O. King, Jr.; and
U.S. Pat. No. 4,308,736, granted Jan. 5, 1982, to J. R. Lowe at al.